Patrick, is an Agilent 34401A good enough? Eventually even 4 wire probe.
Not calibrated every year anyway.
As you were kind enough to offer your nice design to the forum, can you briefly descibe the power supply you are using? A custom 650 VA xfrm (12+12V I guess) and then?
Thank you!
Not calibrated every year anyway.
As you were kind enough to offer your nice design to the forum, can you briefly descibe the power supply you are using? A custom 650 VA xfrm (12+12V I guess) and then?
Thank you!
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too much dissipation
you need greater bias through halves than original F5 , because each half see just half of load
so - you must decrease PSU voltage because of excessive dissipation
anyway - it's doable , but with doubling outputs and enormous heatsinks
Does the power supply have enough voltage to swing 4A into 8 ohms? Correct me if I'm wrong, but I think you would need 20VDC rectified to get 64W into 8ohms.
Nice power increase! Does this increase gain, or does that remain at 15 db? (Of course I mean with the standard feedback resistors)
Russellc
I'm building a DCB1 buffer (2) boards to feed my balanced F5's. I don't think its super-symmetric, but it's simple and cap free along the signal path. There is a group buy in the works that ends on Sunday.
Meaurement of a Vishay Dale CPF3 0.47 Ohm resistor, with Fluke meter
Here are the results of 10 readings taken of a single resistor
0.467, 0.467, 0.467, 0.466, 0.466, 0.465, 0.466, 0.465, 0.466, 0.465
Average 0.466
Standard Deviation 0.000816
It’s not better than 0.1% but it’s not bad either.
I would be interested to see how it compares to your method.
If you can elaborate I will do it just to satisfy my curiosity.
Here are the results of 10 readings taken of a single resistor
0.467, 0.467, 0.467, 0.466, 0.466, 0.465, 0.466, 0.465, 0.466, 0.465
Average 0.466
Standard Deviation 0.000816
It’s not better than 0.1% but it’s not bad either.
I would be interested to see how it compares to your method.
If you can elaborate I will do it just to satisfy my curiosity.
thanh,
Zen Mod & I are simply trying to tell you a professional way of measuring small value resistors reliably.
If you think your method is good enough for you, that's fine with me. There is no challenge, as there is no price for me to win.
If you want to compare the 2 methods, send me a email and I tell you how. You are welcome to publish the results. It is just much more reliable by principle and less subjected to errors. Check out what a 4-lead resistor does, like those from Isabellehuette, e.g.
As to power supply, as said I design for 6 ohm. Dissipation per FET max 32V. That gives 16Vx2A bias per FET. Max output to load is theoretically 32V (rail to rail for balance circuits), 4A (2x bias), or 64W 8ohm (sine). But I (and Nelson) normally leave 4V Vds minimum to avoid excessive nonlinear behaviours of the FETs, which reduce to 24V 4A, or 48W 6ohm (sine).
4 FETs 32W makes 128W. Factor of 3 for toroidal means 384VA min. I said I use 650VA, because it fits the housing. You can use 400VA or 500VA as you like. No real issue, but also not much price difference.
You can change voltage / current according to your own needs (at your own risk). Just make sure you don't cook the FETs.
Am still looking for EU-based volunteer to organise GB for source resistors. If all fails then thanh gets the job, and I only do the buying. Only helping me with matching and distributing (one anonymous offer) is still too much burden for me. But thank you very much for the offer anyway, JB.
Patrick
Zen Mod & I are simply trying to tell you a professional way of measuring small value resistors reliably.
If you think your method is good enough for you, that's fine with me. There is no challenge, as there is no price for me to win.
If you want to compare the 2 methods, send me a email and I tell you how. You are welcome to publish the results. It is just much more reliable by principle and less subjected to errors. Check out what a 4-lead resistor does, like those from Isabellehuette, e.g.
As to power supply, as said I design for 6 ohm. Dissipation per FET max 32V. That gives 16Vx2A bias per FET. Max output to load is theoretically 32V (rail to rail for balance circuits), 4A (2x bias), or 64W 8ohm (sine). But I (and Nelson) normally leave 4V Vds minimum to avoid excessive nonlinear behaviours of the FETs, which reduce to 24V 4A, or 48W 6ohm (sine).
4 FETs 32W makes 128W. Factor of 3 for toroidal means 384VA min. I said I use 650VA, because it fits the housing. You can use 400VA or 500VA as you like. No real issue, but also not much price difference.
You can change voltage / current according to your own needs (at your own risk). Just make sure you don't cook the FETs.
Am still looking for EU-based volunteer to organise GB for source resistors. If all fails then thanh gets the job, and I only do the buying. Only helping me with matching and distributing (one anonymous offer) is still too much burden for me. But thank you very much for the offer anyway, JB.
Patrick
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I got interested to see how good these Dale CPF3 resistors are.
I increased the temperature to 60 degrees (RT=20 degress) and I got immeasurable temperature change. That is if there was any change it was below the resolution of the meter (<1 mOhm)
So TCR is better than (or less than) (1x1000000)/(466x40) = 53.6ppm
This is much better than the manufacturers spec sheet.
I will do these measurement again with better instrumentation and at higher temperatures to get more accurate results.
I increased the temperature to 60 degrees (RT=20 degress) and I got immeasurable temperature change. That is if there was any change it was below the resolution of the meter (<1 mOhm)
So TCR is better than (or less than) (1x1000000)/(466x40) = 53.6ppm
This is much better than the manufacturers spec sheet.
I will do these measurement again with better instrumentation and at higher temperatures to get more accurate results.
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